Desulfurization of residual crudes



United States Patent 3,320,156 DESULFURIZATION OF RESIDUAL CRUDES Maurice Amedee Bergougnou, Madison, N.J., assignor to Esso Research and Engineering Company, a corporation of Delaware No Drawing. Filed Nov. 16, 1964, Ser. No. 411,629 Claims. (Cl. 208244) The present invention concerns an improved process for removing sulfur from petroleum fractions. The invention relates to an improved process for removing sulfur from hydrocarbon fractions containing sulfur compounds by contacting said fractions with cobalt hydroxide at elevated temperatures to form cobalt sulfide. The sulfides settle in the treated hydrocarbon fraction, are separated, regenerated, and recycled to the process.

The problem of sulfur removal from petroleum fractions and crudes goes back to the inception of the petroleum industry. For most urposes, it is undesirable to have an appreciable amount of sulfur in any petroleum product. Gasoline should be relatively sulfur-free to make it compatible with lead, Motor fuels containing sulfur and mercaptans are undesirable because of odor and gum formation characteristics. Sulfur is objectionable in fuel oils because, upon combustion, sulfur dioxide, a corrosive gas having an obnoxious odor, is formed. Metropolitan areas have been particularly conscious of air pollution problems caused by sulfur-containing fuels and, in certain instances, have restricted by law the amount of sulfur permissible in the fuel oils utilized in the locale.

Generally, sulfur appears in feed stocks in one of the following forms: mercaptans, hydrogen sulfide, sulfides, disulfides, and as part of complex ring compounds of which thiophene is a prototype. The mercaptans are more reactive and are generally found in tthe lower boiling fractions, e.g. gasoline, naphtha, kerosene and light gas oil fractions. Well-known processes for sulfur removal from these lower boiling fractions have been suggested such as doctor sweetening (wherein mercaptans are converted to disulfides), caustic treating (where aqueous solutions of sodium hydroxide are used), solvent extraction, copper chloride treating, etc., all give a more or less satisfactory decrease in sulfur or inactivation of mercaptans by conversion into disulfides. When the process results in the formation of disulfides, the disulfides generally remain in the treated product and must be removed by another step if it is desired to obtain a sulfur-free product.

Sulfur removal from higher boiling fractions, however, has been a more difficult problem. Here, sulfur is present for the most part in the less reactive forms as sulfides, disulfides, and as part of the complex ring compounds of which thiophene is a prototype. Such sulfur compounds are not susceptible to conventional chemical treatment found satisfactory for the removal of mercaptans and hydrogen sulfide. Extraction processes employing sulfur selective solvents are usually unsatisafctory because the high boiling petroleum fractions contain such a high percentage of sulfur-containing molecules. For example, even if a residuum contains only 3 wt. percent sulfur, it is possible that substantially all of the molecules may contain sulfur. Thus, if such a residuum were extracted with a solvent selective to sulfur compounds, the bulk of the residuum would be extracted and lost.

stantially ineffective in removing sulfur compounds particularly from the higher boiling fractions.

In accordance with the present invention, cobalt hydroxide is contacted with a sulfur-containing hydrocarbon fraction at mildly elevated temperatures and suflicient pressure to maintain a liquid hydrocarbon phase. The sulfur in the hydrocarbon compounds reacts with the metal hydroxides to form metal sulfides which settle from the treated hydrocarbon fraction. The settled sulfides and any unreacted hydroxides are removed from the treated fraction. The metal sulfide is separated and washed and can be regenerated in a number of ways.

Many advantages accrue to the process of the present invention in using this particular reagent for carrying out the desulfurization step. Desulfurization can be carried out at temperatures of 500-750 F., and can be carried out at about atmospheric pressure. The degree of desulfurization with this reagent under these mild conditions is sufiicient to make the process both practical and economical. One of the primary advantages of using cobalt hydroxide, however, is in that this particular reagent is substantially more easily regenerated than other reagents suggested for removing sulfur compounds from hydrocarbon fractions.

The desulfurization reagent used in accordance with the present invention is cobalt hydroxide. The reagent is used in finely-divided form. The cobalt hydroxide has an amorphous colloidal or fluffy appearance. The preferred form for the hydroxide is a colloidal unflocculated sus pension. However, in practice, some coagulation takes place during hydroxide preparation, e.g., regeneration. The reagent can be used as an aqueous suspension or the moist hydroxide can be dispersed in light hydrocarbon liquids. The cobalt hydroxide is insoluble in both water and petroleum hydrocarbons.

In accordance with the present invention, cobalt hydroxide is contacted with a sulfur-containing hydrocarbon fraction at temperatures of between about 500 and about 750 F. but below the cracking temperature of the feed. Sufficient pressure is used to maintain the hydrocarbon feed in the liquid phase. The sulfur compounds in the hydrocarbon fraction react with the metal hydroxide to form the corresponding metal sulfide. The thus formed metal sulfides settle from the oil and are separated from the oil. The hydroxide, in finely divided form, is contacted with the oil to render the hydroxide readily available for reaction with the sulfur present in the hydrocarbon fraction. The hydroxide is contacted with the hydrocarbon fraction to be treated at a ratio of 0.1/1 to 2.0/1 wt. of hydroxide to hydrocarbon. The contact between the hydroxide and the hydrocarbon fraction is sufiicient to substantially reduce the sulfur content in the hydrocarbon fraction. The contacting can be carried out in a cocurrent, countercurrent, or batch technique. The treated hydrocarbon fraction is subsequently fed to a settling zone wherein the metal sulfides are settled and are separated therefrom.

The metal sulfides recovered from the treated oil can suitably be washed and regenerated to the corresponding metal hydroxide. A preferred technique for regenerating the metal sulfides is to air-oxidize the meal sulfides in an aqueous suspension to the metal sulfates and hydrolyze these sulfates with an aqueous ammonium solution to obtain the corresponding ammonium sulfate and metal hydroxide. Alternately, these two steps of oxidation of the sulfide and hydrolysis of the sulfate can be carried out simultaneously. To do so, the aqueous suspension of sulfide is treated with air and ammonia in a heated vessel under pressure. I

The process has particular application to the removal of sulfur from the heterocyclic sulfur ring compounds in heavy residual hydrocarbon fractions, which sulfur is not removable by conventional techniques, e.g. alkali metal caustic treating processes, which processes are suitable for removing H 8 and rnercaptan compounds from the lighter gasoline fractions. The process, however, can

also be used to remove sulfur from low-boiling hydrocarbons in the gasoline range and intermediate boiling hydrocarbons in the kerosene and fuel oil range.

Several advantages accrue from carrying out the desulfurization process in accordance with the present invention. The sulfur content of high boiling residua fractions can be substantially reduced at moderate temperatures and at atmospheric pressure (with the higher boiling fractions) by using the cobalt hydroxide reagents of the present invention. A distinct advantage of the present process is the ease with which the used cobalt sulfide reagent from the desulfurization step can be regenerated to the hydroxides by conventional methods at reasonable temperatures.

The hydrocarbon desulfurization reagent used in accordance with the present invention is cobalt hydroxide. The hydroxide is preferably used in the finely divided form. The hydroxide is preferably contacted with the hydrocarbon feed to be desulfurized in the moist amorphous or colloidal form, that is, containing various amounts of occluded water.

The desulfurization reaction is carried out at mildly elevated temperatures and preferably at about atmospheric pressure. At about atmospheric pressure, the heated hydroxide releases the occluded water which is vaporized from the hydrocarbon being treated and the finely dispersed hydroxide, per se, is the desulfurization agent. Any hydrocarbon fraction containing H 8, mercaptains, sulfides, or disulfides and/or ring sulfur compounds of which the sulfur atom is a member of the ring can be treated in accordance with the present invention. Therefore, these reagents can be used with light hydrocarbon feeds boiling in the range of ISO-450 F., middle distillates boiling in the range of 450-650 F., heavy hydrocarbons boiling in the range of 650-900 F. and residual fractions boiling in the range of 900-1200 F. plus. The reagent is particularly useful and is especially preferred to be used in treating residual hydrocarbon fractions containing constituents boiling above 900 F., preferably above 950 F. Particular advantage is obtained in using this reagent with the residual hydrocarbon fractions since the conventional desulfurization agents are not suitable for desulfurinzing the heavy residual fractions. The residual fractions boiling above 900 F. will contain up to 2.5 to about 7.0 wt. percent sulfur based on feed. However, feed containing as little as 0.5 to 1 wt. percent sulfur based on feed can also .be treated. Specific feeds that can be treated in accordance with the present invention are gasoline fractions, fuel oil fractions, Kuwait residuum fractions boiling above 900 F. and containing about 5.2% sulfur, 400 F.+ heavy Lake mix fraction containing 2.5% sulfur, 700 F.+ Kuwait residuum containing 4.2% sulfur, 650 F. heavy Lake residuum containing 4.0% sulfur, and the like.

The desulfurization step can be carried out as a batch process, continuous, cocurrent or countercurrent process. Preferably, the process is carried out in a slurry mixture of the hydroxide and the feed to be desulfurized. The desulfurization step is carried out at temperatures below the cracking temperature of the hydrocarbon being treated. The desulfurization step can be carried out at temperatures of 500 to 750 F., more generally 600 to 700 F., and preferably at temperatures of about 600 to 650 F. The hydrocarbon is mixed with the hydroxide at a ratio of 0.1 to 2.0 wt. of hydroxide based on dry hydroxide to wt. of hydrocarbon, more generally at 0.25 to 1.5, and preferably at 0.50 to 1.0. The weight of hydroxide used can be 1.0 to 3.0 multiples of the stoichiometric amount of cobalt needed to remove all of the sulfur present. Contacting is carried out for a sufficient period to substantially reduce the sulfur content of the hydrocarbon being treated. Treating times of hour to 16 hours can be used, more generally /2 to 8 hours and preferably holding times of 1 to 4 hours are used. The contacting can be carried out at about atmospheric pressure and with light feeds up to pressures sutficient to maintain the hydrocarbon in the liquid phase. However, the pressure at which the contacting is carried out is not particularly critical. The pressure should be such that the water occluded with the hydroxide can vaporize although vaporization of the water is not mandatory.

When contacting heavy viscous residual fractions, it may be desirable to add to the hydrocarbon to be treated light diluents such as C -C hydrocarbon fractions. Other diluents such as a light naphtha fraction boiling in the range of -450" F. can be used. These fractions are easily separated from the residual fractions by low temperature distillation. The addition of light diluents substantially lowers the viscosity of the heavy residual fractions and brings about more efficient contact between the finely divided hydroxide and the hydrocarbon fraction, thereby facilitating desulfurization of the hydrocarbon fraction being treated. The reaction vessel should be provided with a suitable mixing means to obtain efficient contact between the hydroxide and feed.

In accordance with the preferred embodiment of the present invention, a 950 F.+ Kuwait residua feed having 5.2 wt. percent sulfur based on feed is contacted with amorphous cobalt hydroxide. The hydroxide is dispersed throughout the feed. At the mixing temperature of about 200 F., the hydroxide is moist and contains some 00- cluded water. The hydroxide is gently mixed with the residual feed. The hydroxide is added at a ratio of about 1.0 wt. of hydroxide to residuum based on wt. of dried cobalt hydroxide. The temperature of the hydroxide and residuum is then gradually increased to a temperature of about 650 F., at which temperature it is held for a period of about 2-4 hours, whereby the sulfur concentration of residuum is decreased by about 45%. The sulfur compounds in the residuum react with the cobalt hydroxide to form cobalt sulfide which separates in finelydivided form. During the heating step from 200 to about 500 F the occluded water with the hydroxide vaporizes from the residual fraction being treated. The reaction products containing unreacted hydroxide, cobalt sulfide, and desulfurized oil is fed to a settler wherein the cobalt sulfide and unreacted cobalt hydroxide are settled and separated from the treated residuum.

Settling can be enhanced by the addition, particularly with viscous feeds, of a light hydrocarbon diluent which lowers the viscosity of the oil and increases the settling rates of the cobalt sulfide and of the unreacted cobalt hydroxide. The separated cobalt sulfide and cobalt hydroxide can be withdrawn from the bottom of the reactor and/or the treated liquid can be withdrawn from the top of the reactor in a conventional manner. Settling aids, such as electrical precipitators and bafile plates and centrifuges, etc., can be used to aid in the separation. The thus treated hydrocarbons, either before or after separation of the solids, are cooled to about ambient temperature and, after removal of the sulfide, can be water-washed to remove any residual amounts of hydroxides and/or sulfides. The withdrawn cobalt sulfide and cobalt hydroxide are water-washed to remove residual hydrocarbons and are treated to regenerate the cobalt sulfide to cobalt hydroxide.

The recovered hydrocarbon fraction is reduced in sulfur content from about 5.2 wt. percent to about 2.9 wt. percent, based on feed. This treated hydrocarbon could be subjected to a second desulfurization step or it can be blended with hydrocarbon fractions containing substantially no sulfur to obtain a blended hydrocarbon fraction of less than about 2.5% sulfur which is acceptable for most uses.

In a preferred embodiment of the present invention, the cobalt sulfide separated from the treated hydrocarbon is washed with a light hydrocarbon solvent stream, for example, light naphtha, steam stripped and then dispersed in water. The suspended sulfides are oxidized by bubbling air through the water to obtain water soluble cobalt sulfate. This step can be carried out in an autoclave at temperatures of ZOO-300 F. and at pressures of 100-200 p.s.i.g. The oxidation step is carried out for a period of 1-2 hours. The solution of cobalt sulfate obtained is then cooled and contacted with an aqueous solution of ammonia, air is bubbled through the aqueous solution, and the cobalt sulfate is hydrolyzed to cobalt hydroxide. In this manner, a fluffy metal hydroxide reagent containing occluded water is produced. The metal hydroxide slurry is uncoagulated and partly colloidal in form and generally has an amorphous appearance. The regeneration step can be carried out in one step in which case the cobalt sulfide is digested with an ammonia solution and air in a vessel at 200 to 300 F. under pressure.

The hydroxide produced is separated from the ammonia solution, water-washed to remove residual ammonia and/ or ammonium sulfate, and then is recycled to the process and contacted with the hydrocarbon feed at Example 1 In order to show the effectiveness of the cobalt hydroxide reagent for desulfurization of a residuum fraction, the following tests were carried out. These tests also compare applicants cobalt hydroxide with other reagents, such as manganese oxide, iron hydroxide and iron oxide. The hydrocarbon feed used consisted of a 950 F.+ Kuwait residuum which contained 5.2 wt. percent sulfur. The desulfurization step was carried out at temperatures of 600 to 650 F. for periods of contact of 2-4 hours. The contacting was carried out at atmospheric pressure. The hydroxide was added in the form of moist amorphous hydroxide. In carrying out the process, the prescribed amount of reagent (dry weight of hydroxide) based on weight of oil, was admixed in a slurry and heated for the indicated amount of time at the indicated temperature. The results of the tests are indicated below in Table I.

TABLE I.DESULFURIZATION OF KUWAIT RESIDUUM vWITH METAL OXIDES AND HYDROXIDES Wt. Percent Metal Temp, Time, Percent Reagent Reagent on Equiv. on Oil F. hrs. Sulfur Oil Removed .the oil. After separation of the aqueous solution of ammonium sulfate, the residuum containing the dispersed colloidal cobalt hydroxide is gradually heated to the treating temperature as heretofore stated. Although ammonium sulfate can be decomposed'by heating to regenerate the ammonia gas, it is preferable to neutralize the solution, e.g. with lime. Ammonia is liberated and recycled to the sulfide digestion step.

Another technique for regeneration of the cobalt sulfide is to mix the cobalt sulfide with cobalt tri-chloride at elevated temperatures and pressures to obtain cobalt dichloride and free sulfur, separating cobalt dichloride from the free sulfur, and hydrolyzing it in the presence of water and oxygen to obtain the cobalt hydroxide and cobalt trichloride. Cobalt hydroxide is separated from the cobalt chloride and recycled to the desulfurization process.

Other means of converting sulfide to cobalt hydroxide, known in the art, can be used.

The following examples are given to illustrate the preferred embodiments of the invention.

The above data clearly show that cobalt hydroxide is an unexpectedly superior metal desulfurization agent and efficiently and effectively carries out the desulfurization of the heavy residuum fraction. The above data'also shows that manganese oxide, iron hydroxide and iron oxide are relatively inefficient desulfurization agents.

In carrying out the above desulfurization step, the cobalt sulfides are settled from the treated oil, are separated from the treated oil, and are regenerated in accordance with one of the above described techniques. A residuum of decreased sulfur concentration is recovered.

Example 2 To further illustrate the unique properties of cobalt hydroxide, several additional tests were carried out wherein other metals, such as iron, copper, barium, calcium, strontium and hydroxides and/or their oxides, were used in the same manner as the cobalt hydroxide of the present invention to carry out a desulfurization process. In this example, a 950 F.+ Kuwait residium containing 5.2. wt. percent sulfur was treated for 2-4 hours at temperatures of 600-700 F. In each case, the hydroxide or oxide was added as finely divided material to the hydrocarbon to be treated to form a slurry of the hydrocarbon and the hydroxide or oxide reagent. After the period of time indicated for the treatment, the metal sulfide and unreacted hydroxide or oxide were separated from the hydrocarbon, and the amount of sulfur removed was determined. In each case, the moist hydroxide reagent was added to the oil being treated. The oxides were added as finely divided solid material.

The results obtained from the test are shown below in Table II.

TABLE II.DESULFURIZATION OF 950 F.+ KUWAIT RESIDUUM WITH COBALT, METAL OXIDES AND HYDROXIDES 1 Excessive coke formation.

The above data clearly show the unique desulfurization properties of cobalt hydroxide in desulfurizing a heavy residuum fraction. The cobalt hydroxide is far superior to the other metal oxides and hydrovides. The copper hydroxide, though eflicient in desulfurization, results in the formation of excessive coke which makes for a substantial loss of the product. The barium and calcium hydroxide as well as strontium hydroxide are relatively inefficient in separating sulfur from the residuum fraction.

Applicant has unexpectedly found that the cobalt hydroxide of the present invention is uniquely suitable for removing sulfur from sulfur compounds in residuum fractions. These sulfur compounds are more difficult to remove than mercaptans, hydrogen sulfide, sulfides or disulfides from the lighter fractions. Though the examples specifically illustrate removal of sulfur from heavy fractions and though cobalt has particular advantages in removing sulfur from heavy fractions, the same reagent can also be used to remove sulfur from lighter fractions.

The invention is not to be limited by any theory regarding its operation nor is it to be limited by the spe cific examples herein presented nor the specific embodiments herein described. The scope of the invention is to be determined by the appended claims.

What is claimed is:

1. The process for removing sulfur impurities from a hydrocarbon fraction containing from 0.5 to 7.0 wt. percent sulfur which comprises contacting said fraction at a temperature in the range of 500750 F. with a reagent consisting essentially of cobalt hydroxide and recovering a fraction of substantially reduced sulfur content.

2. The process of claim 1 wherein the hydroxide reagent is contacted with said hydrocarbon at a ratio of 0.1/1 to 2.0/1 of hydroxide to hydrocarbon, said hydroxide being based on weight of dry hydroxide.

3. The process of claim 1 wherein the contacting is carried out for a period of /2 to 8 hours.

4. The process of claim 1 wherein said hydroxide is colloidally dispersed in the hydrocarbon.

5. A- process for removing sulfur impurities from a hydrocarbon fraction containing constituents boiling above about 950 F. which comprises mixing said fraction in a liquid phase at about atmospheric pressure with a reagent consisting esesntially of cobalt hydroxide at a temperature of to 300 F., gradually increasing the temperature of the mixture to about 600 to 700 F., maintaining said latter temperature until the sulfur concentration of said fraction is substantially reduced by conversion of the cobalt hydroxide to cobalt sulfide and subesquently separating the cobalt sulfide from said fraction.

6. The process of regenerating cobalt hydroxide hydrocarbon desulfurizing agent containing cobalt sulfide which comprises dispersing said reagent in water, oxidizing said sulfide to water soluble sulfate by contacting said sulfide with an oxidizing agent, contacting said sulfate with an aqueous solution of ammonia and an oxygen-containing gas, hydrolyzing the cobalt sulfate to cobalt hydroxide, forming in situ cobalt hydroxide, and separating said regenerated hydroxide reagent from said aqueous solution.

7. The process of claim 6 wherein the reagent prior to regeneration is washed with a solvent and steam stripped prior to dispersing it in water.

8. The process of claim 6 wherein the oxidation step is carried out by bubbling air through said dispersion.

9. The process of claim 6 wherein the oxidation step is carried out at temperatures of 200 to 300 F. and at pressures of 100 to 200 p.s.i.g.

10. The process of claim 6 wherein the oxidation of the sulfide and the formation of the hydroxide are carried out in a single step by bubbling air and ammonia gas through the aqueous sulfide suspension in a vessel maintained at a temperature of 200 to 400 F. and a pressure of 100 to 200 p.s.i.g.

References Cited by the Examiner UNITED STATES PATENTS 2,177,343 10/1939 Hughes 208-249 2,422,875 6/1947 Agren 208--249 2,616,834 11/1952 Leutz 208244 2,618,586 11/1952 Hendel 208-249 3,063,936 11/1962 Pearce et al. 208-244 DELBERT E. GANTZ, Primary Examiner.

S. P. JONES, Assist nt Examiner. 

1. THE PROCESS FOR REMOVING SULFUR IMPURITIES FROM A HYDROCARBON FRACTION CONTAINING FROM 0.5 TO 7.0 WT. PERCENT SULFUR WHICH COMPRISES CONTACTING SAID FRACTION AT A TEMPERATURE IN THE RANGE OF 500-750*F. WITH A RECOVERILNG A FRACTION OF SUBSTANTIALLY REDUCED SULFUR CONTENT. 